3.2 chromosomes

Question 1

how is the genetic material in prokaryotes stored

Answer 1

• free in NUCLEOID (no nucleus)
• prokaryote DNA (‘naked dna’)
  
  • single chromosome, circular DNA (not associated w proteins for additional packaging)

Question 2

what cells have plasmids?

Answer 2

some prokaryotic cells
(Plasmids are additional circular DNA molecules)

Question 3

what are plasmids?

Answer 3

small, circular DNA
- may contain one or several genes
- bacteria can easily exchange plasmids
- can self-replicate

Question 4

steps to become eukaryote chromosomes 5

Answer 4

1. dna coiled around 8 histone proteins – nucleosome
2. nucleosomes linked by additional histone protein – string of chromatosomes
3. coil to form solenoid structure – condensed to form 30 nm fibre
4. fibres form loops, compressed and folded around proteins to form chromatin
5. chromatin supercoil during cell div into chromosomes

Question 5

what is the constriction point??? of a chromosome. and what are the shorter and longer sections called

Answer 5

centromere
shorter section – p arm
longer section – q arm

Question 6

how can the unique banding patterns on chromosomes be generated

Answer 6

staining

Question 7

what is a locus

Answer 7

a position of a particular gene on a chromosome

Question 8

three points of reference for the region of a locus

Answer 8

1. number/letter that denotes WHICH CHROMOSOME
2. which ARM the locus is on (q or p)
3. number corresponding to the G BAND location

Question 9

what are organismms wtih TWO sets of chromosomes called

Answer 9

diploid

Question 10

diploid divided by 2 =

Answer 10

haploid (sex cells/gametes)

Question 11

what is a zygote

Answer 11

a diploid cell resultant from the fusion of 2 gametes

Question 12

characteristics of a diploid nuclei

Answer 12

• nuclei possessing PAIRS of HOMOLOGOUS chromosomes (2n)
• two alleles for each trait
• all body/somatic cells are diploid

Question 13

characteristics of haploid nuclei

Answer 13

• only 1 set of chromosomes (n)
• possess a SINGLE allele for each trait
• all gametes are haploid (from diploid cells via meiosis)

Question 14

characteristics of homologous chromosomes

Answer 14

• carry same set of genes in diff locations
• each allele (diff versions of the same gene) comes from each parent

Question 15

what are alleles

Answer 15

diff versions of the same gene

Question 16

what are the common stuff between homologous chromosomes

Answer 16

• same structural features
• same genes at the same loci (may have diff allele

Question 17

what is a karyotype

Answer 17

the number and types of chromosomes
in a eukaryotic cell

Question 18

method karyotypes are determined

Answer 18

1. harvesting cells from foetus or WBC
2. chemically inducing cell division, arresting mitosis while chromosomes are condensed
   (stage halted will determine if the chromosomes appear w sister chromatids)

Question 19

how does a karyogram work

Answer 19

(it looks like all the homogolous chromosomes but 1-22 + x and y)
- chromosomes stained and photographed
- chromosomes arranged into homologous pairs according to size

Question 20

why cant species interbreed

Answer 20

• diff diploid numbers – cannot form homologous pairs in zygotes
• offspring are infertile, cannot form functional gametes

Question 21

heterosomes vs autosomes

Answer 21

heterosomes: determines sex
autosomes: does not

Question 22

why karyotype an unborn child

Answer 22

• determine gender
• test for chromosomal abnormalities

Question 23

down sydrome

Answer 23

• 3 pairs of chromosome 21
• caused by non-disjunction event
• mental and physical delays in development

Question 24

what is a non-disjunction event?

Answer 24

seperation fails – both sister chromatids/homologous chromosomes are pulled to same pole

Question 25

genome size comparison: viruses and bacteria, prokaryotes, eukaryotes, plant

Answer 25

viruses and bacteria: very small
prokaryotes: smaller than eukaryotes
plant: varied (plants can self fertilise)

Question 26

what is the technique for meausring length of DNA molecules and who founded it

Answer 26

autoradiography
john cairns

Question 27

what does autoradiography do

Answer 27

for measuring the length of DNA molecules
- visualise chromosomes whilst uncoiled

Question 28

old method to find chromosome length that was inaccurate

Answer 28

measured while condensed during mitosis – inaccurate due to supercoiling

Question 29

what did cairns technique discover about DNA replication 2

Answer 29

• DNA replication involves formation of a replication bubble (while prokaryotic involves a single origin of replication)
• DNA replication is bi-directional (occurs independently at both ends of replication bubble)

Question 30

cairns technique steps (6 steps)

Answer 30

1. cells grown in solution with RADIOACTIVE THYMIDINE
2. tritiated thymidine is INCORPORATED into CHROMOSOMAL DNA
3. chromosomes are isolated by LYSING the cells fixing the chromosomes to a photographic surface
4. RADIATION released converts Ag+ IONS in SILVER BROMIDE into INSOLUBLE metal grains
5. EXCESS silver bromide is washed away, leaving silver grains as SMALL BLACK DOTS
6. when the film is developed, chromosomal DNA can be VISUALISED with a ELECTION MICROSCOPE

Question 31

identifying gene loci and its polypeptide product using databases?? name the 2 (i dont know why youd need this)

Answer 31

genbank / omim